Unie Van Kunstmestfabrieken B.v.

Dsm IP Assets B.v.

Stamicarbon B.v.

Andreas J Biermans

Kees Jonckers

Petrus J Van Nassau

Henk C Burks

Johannes Henricus Mennen

Nora Anna De Wit

Bastiaan Renè Agnes Marie Van De Kerkhove

Karel G Raemaekers

Herbert Willem Gerrit Hooijkaas

Mario G De Cooker

The invention relates to a process for separating NHfrom a mixture containing NH, COand HO which comprises an NHrectification step carried out in a NHseparation device to which one or more streams containing NH, COand HO including the mixture, are supplied, with a stream consisting substantially of gaseous NHbeing formed in the NHseparation device, separated from the mixture and discharged. In the process according to the invention a condensation step is carried out on at least one of the stream consisting substantially of gaseous NHor the one or more streams containing NH, COand HO supplied to the NHseparation device, in which at least a part of the existing COis converted to a liquid phase.

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Process for the preparation of urea from ammonia and carbon dioxide in which all or part of the liquid ammonia needed for the process is supplied to the high-pressure scrubber in such a way that it is in direct contact with the other streams supplied to this scrubber. In particular in such a way that there is direct contact between the liquid ammonia and the off-gases transferred to the high-pressure scrubber from the urea synthesis reactor. More in particular in such a way that there is direct contact between the liquid ammonia and the off-gases transferred to the high-pressure scrubber from the urea reactor and with the carbamate stream, which is transferred from the low-pressure urea recovery section.

Process for the preparation of urea

A method and apparatus for determining the saturation temperature of a solution containing a dissolved substance, the crystals of which are optically anisotropic. The solution is placed in an optical measurement vessel under conditions wherein crystals of said substance are present, and the temperature of said crystal containing solution is gradually increased to at least the temperature at which all of the crystals dissolve. The temperature of the solution is continuously measured. Simultaneously with the temperature increase, a beam of linearly polarized light is directed into the optical measurement vessel in a manner such that it is transmitted through said solution; the transmitted beam of light, after having passed through the solution, is directed through a light polarizing analyzer having a direction of polarization normal to that of said beam of light; and at least a portion of any light transmitted through said analyzer is directed to a light measuring photodetector. Any light passing through crystals while present in the solution is optically rotated such that it is transmitted through the analyzer to the measuring photodetector, and the intensity of the transmitted light reaching said photodetector decreases to a lower, substantially constant level when all of the crystals have dissolved. The saturation temperature is the temperature of the solution at the time the light measured by the photodetector reaches this lower, substantially constant level.

Method and apparatus for determining the saturation temperature of a

A process for determining the composition of an aqueous solution of ammonia and carbon dioxide from which ammonium carbamate or ammonium carbonate crystallizes out upon cooling to below the saturation temperature. The density and the saturation temperature of the solution are measured, and the ammonia, carbon dioxide, and water composition is determined by reference to densities and saturation temperatures of aqueous solutions of ammonia and carbon dioxide of known composition. The composition thus determined can be used to effect control over the composition of such aqueous solutions.

Process for determining and controlling the composition of aqueous

An improved process for the preparation of urea from carbon dioxide and excess ammonia at elevated temperature and pressure. The urea solution from the urea synthesis zone is heated and stripped at an elevated pressure to decompose a portion of the ammonium carbamate contained therein and the ammonium and carbon dioxide containing off-gas produced is condensed in a first condensation zone. The stripped urea solution is heated at a reduced pressure in a decomposition zone to decompose a further portion of ammonium carbamate, and the ammonia and carbon dioxide containing off-gas thereby produced is condensed in a second condensation zone to form an aqueous ammonium carbamate solution. A portion of this aqueous carbamate solution is introduced into a desorption zone so as to produce an off-gas more concentrated with respect to ammonia and carbon dioxide than the ammonium carbamate solution, and the off-gas from this desorption zone is condensed into a further portion of such aqueous ammonium carbamate solution in a third condensation zone, maintained at a pressure between the pressure in the decomposition zone and about 40 bar, to form a more concentrated ammonium carbamate solution which is recycled to the urea synthesis zone.

An improved process for the separate recovery of substantially pure ammonia and substantially pure carbon dioxide from mixtures containing ammonia and carbon dioxide, and possibly water, such as are obtained as by-products in the manufacture of melamine from urea or the synthesis of urea from ammonia and carbon dioxide. The by-product mixture is introduced into a process loop having an ammonia separation zone, a carbon dioxide separation zone and a desorption zone, the zone to which the mixture is initially fed being dependent upon its composition. The separation is effected by maintaining a system pressure differential between the ammonia and carbon dioxide separation zones, or adding diluting water to the carbon dioxide separation zone. The efficiency of the separation is enhanced by introducing an ammonia containing gaseous phase into the bottom of the carbon dioxide separation zone.

Process for the separation of NH.sub.3 and CO.sub.2 from mixtures of NH.sub

An improved process for the separate recovery of substantially pure ammonia and substantially pure carbon dioxide from mixtures containing ammonia and carbon dioxide, and possibly water, such as are obtained as by-products in the manufacture of melamine from urea or the synthesis of urea from ammonia and carbon dioxide. The by-product mixture is introduced into a process loop having an ammonia separation zone, a carbon dioxide separation zone and a desorption zone, the zone to which the mixture is initially fed being dependent upon its composition. An ammonia off-gas, substantially free of carbon dioxide and water, is obtained from the ammonia separation zone, and the residual liquid phase is introduced into the carbon dioxide separation zone. Diluting water is also added to the carbon dioxide separation zone in an amount of from about 0.2 to 6 times, by weight, the combined total weight of the residual liquid phase from the ammonia separation zone and the by-product mixture, if any, fed into the carbon dioxide separation zone. A carbon dioxide off-gas, substantially free of ammonia and water, is obtained from the carbon dioxide separation zone and the residual liquid phase therefrom is introduced into the desorption zone wherein substantially all of the ammonia and carbon dioxide are desorbed and separated from the liquid phase and introduced into the ammonia separation zone.

Process for separation of ammonia and carbon dioxide

An improved process for the preparation of urea from carbon dioxide and ammonia at elevated temperature and pressure whereby unconverted ammonia, substantially free of carbon dioxide and water is recovered from a urea and ammonium carbamate containing liquid process stream. An urea and ammonium carbamate containing process stream is expanded to a pressure of between about 1 and 25 kg/cm.sup.2 absolute and heated, thereby decomposing ammonium carbamate and forming a gas mixture containing ammonia, carbon dioxide and water vapor. The improvement comprises the steps of (a) introducing this gas mixture into a carbon dioxide separation column along with sufficient diluting water to form a first residual liquid phase, containing ammonia, carbon dioxide and from about 65 to 96 percent by weight water, in the bottom of such column, and separately removing therefrom an off-gas of carbon dioxide substantially free of ammonia, and the first residual liquid phase; (b) introducing this first residual liquid phase into a desorption column wherefrom a second off-gas containing ammonia, carbon dioxide and water vapor, is removed; (c) introducing the second off-gas into an ammonia separation column and separately removing therefrom a third off-gas of ammonia substantially free of carbon dioxide and water vapor, and a liquid phase containing ammonia, carbon dioxide and water; and (d) recycling the third gas phase back to the urea synthesis zone. The carbon dioxide separation column, desorption column and ammonia separation column are all operated at substantially the same pressure of between about 1 and 25 kg/cm.sup.2 absolute.

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Urmond, Netherlands

Andreas J Biermans